Field of the Invention
The present invention relates to a honeycomb body having a plurality of honeycombs, preferably for use as a catalyst carrier body in motor vehicles. A coating of catalytic material applied to walls of the honeycombs permits conversion of exhaust gases from internal combustion engines.
International Publication No. WO 90/08249, corresponding to U.S. Pat. No. 5,157,010, as well as International Publication No. WO 96/09892, corresponding to U.S. patent application Ser. No. 08/824,443, filed Mar. 26, 1997 and U.S. Pat. No. 5,795,658, describe honeycomb bodies with macrostructures which determine the honeycomb form. The honeycomb bodies additionally have microstructures which influence the flow of exhaust gas passing through the honeycombs.
Honeycomb walls of the bodies are formed of, for example, of metal. A possible way of producing honeycomb bodies with such honeycomb walls includes brazing or welding. Suitable kinds of welds are known, for example, from International Publication No. WO 89/07488.
It is known from European Patent Application 0 229 352 A1 to use a heat radiation guard or protection device. The heat radiation guard or protection device includes one or more sheet layers which are disposed outside a tubular casing. That configuration uses the same sheet layers which also form the honeycomb structure within the tubular casing.
Particularly in the automobile industry, the requirements imposed in terms of the properties of an exhaust gas catalytic converter are becoming ever increasingly strict. In the course of ever increasing strictness in relation to exhaust gas standards, the cold-start and re-start characteristics in particular have to be continually improved. When an engine is re-started after a stoppage time, it is important that the honeycomb body of the catalytic converter still be at a temperature which is as high as possible. International Publication No. WO 96/07021, corresponding to U.S. patent application Ser. No. 08/808,784, filed Feb. 28, 1997, describes a catalytic reactor for the conversion of exhaust gases which has a thermal insulation both within as well as outside a casing. An air gap and an insulating mat are mentioned as examples of such insulations.
In the above-mentioned state of the art, the insulation effect is achieved by air or through the use of a solid insulation material. Admittedly air at rest has a lower level of thermal conductivity than known solid insulating materials, but it only impedes the transportation of heat due to radiation to an extremely slight degree. In contrast, a plurality of sheet layers, as have been proposed in International Publication No. WO 96/07021, corresponding to U.S. patent application Ser. No. 08/808,784, filed Feb. 28, 1997, considerably reduces the amount of heat radiation. However, due to their contact locations, the sheet layers form thermal bridges, with the result that once again a considerable degree of heat transportation can occur due to heat conduction.